The primary goal is to make use of state-of-the-art flow cytometric methods combined with genetic techniques and functional analyses to fully characterize recovering hematopoietic derived cell populations following human bone marrow transplantation. Marrow transplantation is chosen as a primary paradigm of the altered cellular pathophysiology in hematopoietic and immunodeficiency states because of data to suggest that reconstitution of the lymphoid system post transplant recapitulates normal immune ontogeny. The secondary goal is to compare cell populations identified in a transplant model with unique cell types that occur in other pathological states involving hematopoietic derived cells. Using newly developed two-and three-color flow cytometric techniques which identify previously unsuspected cell types the surface phenotype of the recovering cells will be fully defined. The in vivo state of activation and of proliferation of these abnormal cell will be established by surface and DNA studies. The donor versus recipient origin of these cells will be established using DNA restriction enzyme mapping and the clonality of the unusual B and T cell subsets will be established by similar techniques. Three newly recognized unusual phenotyped post transplant cells will be studied intensively for function utilizing established bulk immunoassay techniques as well as limiting dilution and cloning methods: (l) a Leu1- Leu2+ T cell; (2) a Leu2+ natural killer cell; and (3) a Leul+ B cell. The unique availability of this model of human reconstitution in which syngeneic normal cell counterparts are uniformly available for the dissection of the functional deficits of abnormal phenotypically well-defined cells will be used to establish the cytolytic, helper and suppressor capabilities of the unusual T and NK cells and moreover the possible role of the Leu1+ B cell in providing help to normal phenotype B cells when inadequate T cell function is present. The unique availability of human split hematopoietic chimeras with respect of B, T and accessory cell HLA type will be used to study the MHC restriction in man of these interactions. The nature of recovering cell lineages in transplants (undertaken with and without donor marrow T cell depletion) involving various histocompatability differences between donor and recipient will be compared with unique cell types identified in other hematopathologic disease states.